Circular polarization has been used for GPS radio wave, satellite radio wave for satellite digital broadcasting and radio wave for ETC and various kinds of circularly polarized antennas have been proposed (See Patent Document 1).
In recent years, the circular polarization has been widely utilized into wireless LAN represented by WiFi, and wireless communication such as WiMAX and UWB for use of middle-range communication, mobile communication etc. Since a thin and light-weight circularly polarized antenna installed in the wireless communication equipment is required, a planar antenna formed by a printed board etc. is becoming mainstream.
Several wideband planar circularly polarized antennas corresponding thereto have been proposed. For example, non-patent document 1 which the inventors have proposed describes a rectangular antenna element that is obliquely arranged. Non-patent document 2 describes a rectangular antenna element in which a sub pattern of nested structure is formed. Non-patent document 3 describes an antenna element of rectangular loop pattern.
An elliptical antenna element has been known as the wideband planar linearly polarized antenna (see non-patent document 4).